Looking for a strategic partner, what would I expect and be careful about such partnership?

We have a website called powerpik.com, a b2c product promotion platform. As the website is new and doesnt have enough market reach, thought it would be better working with an ad agency as a strategic partner so their current clientele or big brand network would be very helpful for the website to reach out the market as desired. The partnering ad / marketing agency would benefit from the special partner (discounted) pricing etc, while the website itself will work on to sell the promotional services to other brand companies or ad agencies. There could be multiple strategic partners though.

In such scenario, what would I look forward in such strategic partnership with an ad / marketing agency? Any one had experience or any pitfalls in it? Would be greatly appreciated if you could share your experience and/or advice.